InterviewSolution
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Evaluate the following limit :\(\lim\limits_{\text x \to a}\left\{\cfrac{sin\,\text x}{sin\, a}\right\}^{\cfrac{1}{\text x-a}} \)lim(x→0) {sin x/sin a}1/(x - a) |
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Answer» As we need to find\(\lim\limits_{\text x \to a}\left\{\cfrac{sin\,\text x}{sin\, a}\right\}^{\cfrac{1}{\text x-a}} \) lim(x→0) {sin x/sin a}1/(x - a) We can directly find the limiting value of a function by putting the value of the variable at which the limiting value is asked if it does not take any indeterminate form (0/0 or ∞/∞ or ∞-∞,1∞ .. etc.) As it is taking indeterminate form- ∴ we need to take steps to remove this form so that we can get a finite value. Z =\(\lim\limits_{\text x \to a}\left\{\cfrac{sin\,\text x}{sin\, a}\right\}^{\cfrac{1}{\text x-a}} \) Take the log to bring the power term in the product so that we can solve it more easily. Taking log both sides- {∵ log am = m log a} Now it gives us a form that can be reduced to\(\lim\limits_{\text x \to0}\cfrac{log(1+\text x)}{\text x}=1\) Dividing numerator and denominator by\(\cfrac{sin\,\text x-sin\,a}{sin\,a}\)to get the desired form and using algebra of limits we have- Now it gives us a form that can be reduced to\(\lim\limits_{\text x \to0}\cfrac{sin\,\text x}{\text x}=1\) Try to use it. We are basically proceeding with a hit and trial attempt. ∵ sin (A + B) = sin A cos B + cos A sin B Use the formula-\(\lim\limits_{\text x \to0}\cfrac{sin\,\text x}{\text x}=1\) ⇒ log Z = cot a – 0 ∴ log Z = cot a ∴ Z = ecot a Hence, \(\lim\limits_{\text x \to a}\left\{\cfrac{sin\,\text x}{sin\, a}\right\}^{\cfrac{1}{\text x-a}} \)= ecot a |
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